Propene and butene oligomerization into C6 to C16 olefins (also referred to as higher olefins) are industrially important petrochemical processes. These higher olefins are used for example as intermediates in hydroformylation processes leading to valuable chemicals. The branching degree of the higher olefin and the position of the carbon-carbon double bond determine the reactivity in hydroformylation. Most valuable are linear and little branched oligomers. Olefins with low or medium branching index and alpha-olefins in particular find application in plasticizer and surfactant synthesis. Strongly branched oligomers are less desired but can be added to the gasoline pool.
Solid phosphoric acid (SPA) has been widely used as a catalyst for oligomerization of feedstreams containing alkenes with 2 to 12 carbon atoms. However, SPA produces significant amounts of undesired cracked products, it cannot be regenerated and has to be disposed of at the end of the operation or when its activity is no longer satisfactory. Homogeneous catalysts, especially nickel complexes, are known to yield quasi linear oligomers. An example of a homogeneous process is the Difasol process. Homogeneous catalysts, however, present a problem of catalyst recovery. Heterogeneous nickel catalysts are also used for olefin oligomerization such as in the Octol processes. Nickel catalysts are also sensitive to feed impurities such as sulphur and nitrogen components.
Various zeolites have been proposed as an alternative to SPA or to nickel containing species as oligomerization catalysts. For example, U.S. Pat. No. 4,517,399 reports an olefin oligomerization process in which a feedstock containing olefins is passed over a ZSM-5 zeolite catalyst. U.S. Pat. No. 5,571,768, U.S. Pat. No. 5,612,270, U.S. Pat. No. 5,552,357, U.S. Pat. No. 5,625,104 and U.S. Pat. No. 5,610,112 indicate the use of selectivated forms of ZSM-5 and of other zeolites having a constraint index from 1 to 12, namely, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50 and ZSM-57 in olefin oligomerization. WO 93/16020 discloses an alkene oligomerization process over a zeolite catalyst selected from zeolites of the TON(H-ZSM-22, H-ISI-1, H-Theta-1 H-Nu-10, KZ-2), MTT (H-ZSM-23, KZ-1), MFI (H-ZSM-5), MEL (HZSM-11), MTW (H-ZSM-12) or EUO (EU-1) structure types, H-ZSM57, zeolites of the ferrierite structure family, offretites, H-ZSM-4, H-ZSM-18, zeolite Beta, faujasites, zeolite L, mordenites, errionites and chabazites.
WO 95/22516 discloses an olefin oligomerization process with improved selectivity to certain oligomers. The process is carried out over a catalyst comprising at least one molecular sieve having a refined constraint index greater than 10 and at least one molecular sieve having a refined constraint index within the range of from 2 to 10. Examples of molecular sieves having a refined constraint index greater than 10 include ZSM-22, ZSM-23 and certain ferrierites. Examples of molecular sieves having a constraint index within the range of from 2 to 10 include ZSM-5, 11, 12, 35, 38, 48 and 57, SAPO-11, MCM-22 and erionite.
Heterogeneous acid catalysts such as supported phosphoric acid or zeolites mainly result in branched oligomers. In Angewandte Chemie International Edition 2000, 30, 4376-4379, J. A. Martens and R. Ravishankar reported a process for dimerization of butene over ZSM-57, achieving a conversion level of 89% and a dimer product selectivity of 85.7%. The octene (dimer) fraction mainly comprised dimethylhexenes (76% of the octene fraction). The branching index of the dimer fraction therefore approached a value of 2. In Angewandte Chemie International Edition 2005, 44, 5687-5690, J. A. Martens and W. H. Verrelst reported a study on propene oligomerization over ZSM-22, in which ZSM-22 showed very high propene conversion with high yields of dimer and trimer products. The dimer fraction consisted mainly of methylbranched hexenes, with a significant amount of linear hexenes. Within the trimer fraction, dibranched nonenes were dominant products. When the outer catalyst surface was poisoned with collidine, ZSM-22 even gave a trimer fraction extremely rich in monobranched products (80%) with a significant amount of linear trimers (15%).
There remains a need for alternative oligomerization processes with high conversion, product selectivity and which provide oligomers of high linearity. There further exists a need for alternative catalysts to conventional zeolite, SPA and nickel catalysts that can achieve high conversion, product selectivity and product linearity in oligomerization processes.
WO 03/082780 discloses selectivated ZSM-22 or ZSM-23 molecular sieves as oligomerization catalysts to provide products such as octenes and dodecenes from butene, having low degree of branching and a low amount of hindered double bonds. Oligomerization is preferably carried out at a temperature from 190 to 230° C.
US20040068072 discloses cobalt containing organometallic catalysts for dimerization of olefins. Oligomerization is preferably carried out in the temperature range of 10 to 50° C.
GB1124765, GB1124766, GB1183201, GB1095982, Journal of Catalysis 6, 385-396 and 419-424, Robert Schultz et al. (1966), all teach cobalt containing activated carbon catalysts for oligomerization of olefins. The preferred process temperature ranges from −20 to 90° C.
In Bulletin of Chem. Soc. Jap p. 2597-2601 (1997), Kuznetsov et al. disclose the use of modified FAU type zeolite catalysts. On CoY, CaY, CoX hydrooligomerization takes place. The most preferred catalyst, NiX, is used for selective oligomerization of propylene. CoY is obtained by direct ion exchange of NaY to CoNaY. At about 85% NaY exchange the product was Co3.5Na1Al8Si184O384. CoX was obtained by direct exchange of NaX to CoNaX. At about 65% NaX exchange the product was Co28Na31Al87Si105O384. Oligomerization was carried at out a temperature of at least 190° C.
EP 261730 discloses a method for the dimerization of olefins, in particular olefins having between 4 and 24, and preferably between 10 and 20 carbon atoms, using zeolite X and Y having alkaline metals on 10 to 50% of its exchangeable sites, a bivalent or trivalent metal on 1-30% of its exchangeable sites, and the remainder of the exchangeable sites being acid sites.
Microporous and Mesoporous Materials 103 (2007) p. 1-19, J. Denayer et al. describes the use of zeolite X containing cobalt and calcium for removal of cyclopentadiene from 1-octene. CoCaX is made by exchanging NaX to NaCaX, followed by calcination. The obtained NaCaX is then exchanged to CoCaX. The product is Co34Ca9Al86Si106O384.